The advent of affordable touch sensitive tablets and pens as computer input devices and the availability of more powerful microprocessors and lower cost memory has resulted in increased use of computer systems wherein the primary user input interface is hand formed characters or symbols through a touch tablet, often referred to as "tablet computers" and "clipboard computers".
Although such handwritten character input systems offer a more convenient and intuitive user interface for many purposes, the methods and apparatus used for handwritten character recognition have imposed many constraints which have prevented such systems from realizing their full potential. For example, and although much information for identifying handwritten characters is contained in the individual strokes comprising the characters, many system of the prior art are not effective at extracting and using stroke information, either as part of a dynamic and therefore faster process for recognizing characters or in recognizing the constituent parts of the characters. For example, many handwritten character recognition system of the prior art have difficulty in determining whether a curved or angled stroke in a character is a single stroke or two or more strokes.
As a consequence, many such systems of the prior art typically can perform character recognition only upon completed characters, thereby either slowing the performance of the systems or requiring that the systems be implemented only with the very fastest and most powerful microprocessors in order to keep up with the user input.
Another severe problem of the prior art is that most systems of the prior art identify an input character by comparing the completed input character to possible matching character configurations stored in the system, usually either in a database or generated as required. The very large range of variations in character position, orientation, size, and stroke configuration and proportion that can occur with handwritten characters thereby again either severely limits the system performance or requires the use of very powerful microprocessors with large memories and high capacity disk drives to store or generate and process the libraries of possible character configurations.
Yet another problem of the prior art systems for handwritten character recognition is that, because of the complex processing required for recognition of handwritten characters, many such systems impose restrictions upon the user interface in order to reduce the processing requirements.
For example, many such systems require that the characters be written only into predefined spaces, often referred to as "combs", and in a certain order, and some systems of the prior art even require that the characters be limited to certain stroke configurations, such as block capital letters. Such systems, for example, do not permit a user to go back to an earlier part of a line of characters to enter a new character or symbol or to rewrite, modify or edit an already entered character or string of characters.
A related problem is the entry of system or application commands, such as "save file" or "open file" or "spelling check", and the entry of editing commands, such as "insert", "delete", or "insert space". Because of the complexity of processing required to distinguish such commands from handwritten text, however, many systems of the prior art require that application and system commands and editing commands be entered into specially designated areas of the tablet, and even that the system or application commands and the editing commands be entered in separate areas.
As such, the systems of the prior art do not allow the full realization of a handwritten input system. Such systems do not, for example, permit a user to enter characters in a natural, free form style, or to enter a system or application command through a gesture or symbol or combination of symbols entered at any convenient place on the tablet, or to directly edit text by symbols or marks written directly into the text, such as deleting a character by "scratching out" the character.
The method and apparatus of the handwritten character recognition system of the present invention provides a solution to these and other problems of the prior art.